1. Field of the Invention
The present invention relates to a nitrogen gas supply system for dry-cut working apparatus which supplies nitrogen gas to a machining part or to a tip of a tool attached to a working machine such as a machining center, milling machine, lathe, gear cutting machine, grinding machine, etc.
2. Description of the Related Art
The cooling of a tool attached to a spindle of a working machine in a prior art is carried out by injection of cutting liquid (liquid coolant) from a nozzle of a working machine to a top of the tool, in order to maintain the less friction and the lower temperature of the tool, thereby the effective cutting and the long tool life may be obtained.
In the thus mentioned method of cooling of the tool by using the cutting liquid (liquid coolant), the disposal of sludge is required. However, since the sludge incorporates the perished liquid coolant, it is difficult to dispose of the waste liquid. Further, since the cutting liquid (liquid coolant) is recycled, the liquid may gradually rise in temperature, which may cause thermal expansion of any part of the machine. This is one of the major causes which would spoil the accuracy of machining.
To overcome the above problem, there has been provided a "dry-cut" method which blows non-combustible gas to a working point, as disclosed in the Japanese patent publication after examination (Kokoku) No. Sho 63-62339 or the Japanese patent No. 2568975. In particular, the dry-cut method by non-combustible gas as according to the Japanese patent No. 2568975 has several merits, that the machining part may be being prevented from being oxidized, and that the danger of being ignited due to oil mist may be prevented. However, according to the Japanese patent No. 2568975, the non-combustible gas is supplied from an inert gas tank. Further, according to the above discussed publication No. Sho 63-62339, a tank 11 filled with liquid nitrogen is heated so that the vaporized nitrogen gas may blow out of the tank 11. These system will require more expensive running costs and wider space for installing such a tank. In addition, when the nitrogen gas consumption increases, the replacement of tank or the replenishment of nitrogen gas will frequently be required. Therefore the continuous supply of the nitrogen gas cannot be carried out, thus the machining to workpieces should be disrupted many times.